[The development OF THE vestibular apparatus under conditions of weightlessness]

The spawn of the aquarium fish Brachydanio rerio was developing during 5--6 days under conditions of weightlessness (first on board the spaceship "Sojuz-16", then in the space station "Salut-4") in special aquariums "EMKON", in thermostable installations. Electron microscopically the embryos were found to have a well developed labyrinth in early developmental histologically and cytologically differentiated receptory structures of the macula utriculi and macula saccili. In contrast to controls, the experimental animals showed certain alterations in the otolite organization. In similar experiments the embryos of clawed frog Xenopus laevis in the stage of the tail bud were also placed in special containers "EMKON" and thermostable apparatus "Biotherm-4" and by the spaceship "Sojuz-17" were brought to the space station "Salut-4", where it stayed for 16 days. The initial embryos had already had a well developed acoustic vesicle with macula communis. Inspite of the preliminary load by start acceleration and staying under conditions of weightlessness, they reached the general development fairly similar to controls. As it was shown electron microscopically their labyrinth had highly histologically and cytologically differentiated structures. However, a disturbance of the development of the otolithic membrane and otoconia should be noted. The alterations observed in the otolithic membrane organization in experimental fishes and frogs may be explained by general disorders in calcium metabolism.